Rotational molding and Blow molding are unique processes which offer a number of process advantages. However, it is important to consider the advantages and disadvantages of Roto Molding vs. Blow Molding process when choosing which is right for you.
Rotational molding is versatile process which offers significant design flexibility and a low startup cost. Therefore, the process allows production quantities ranging from 50 units per year going up to 20,000 units per year.
Blow molding is a manufacturing process with shorter cycle times for parts with more limited design flexibility. Initial startup costs are relatively very high.
This article is going to discuss the key aspects of Blow Molding vs. Rotomolding.
See Also Infographic About Rotational molding vs. Blow molding.
Rotational Molding Products
Rotational molding, also referred to as rotomolding is a low pressure thermoforming process which produces seamless small and large hollow plastic products with uniform wall thickness. As a result, the low startup costs make it an ideal process for thermoplastic products.
Products that are rotomolded include single and double wall parts such as kayaks, ice coolers, chassis for electromechanical equipment and marine products. Useful features can be designed into rotomolded parts such as molded-in inserts, spinwelds, colored graphics, foam filling, structural ribs and undercuts. All without welding or bonding pieces together. The ability to produce parts with complex geometry with undercuts and molded-in inserts makes working with rotational molding companies desirable.
See also: 7 Major Plastic (resin) Types for Roto Molding
Blow Molding Products
Blow molding, is a high pressure process which has low cycle times and is ideal for parts with low complexity. Products such as fluid containers, fuel tanks and small plastic toys use the blow molding process. Even though production capacity is high, expensive tooling cost can be a barrier to entry.
In addition, blow molding process has the ability to mold more complex parts, however additional processes such as infra-red welding and heat amplification are required therefore adding cost to the process.
What are the advantages and disadvantages of Blow Molding?
Advantages of blow molding:
- Short cycle times: the cycle time for a blow molded part can range from 5 to 20 minutes but secondary processes such as infra-red welding can sometimes take longer.
- Uniform wall thickness for small parts: parts will have a uniform wall thickness for parts with a small diameter however that can change as the size increases.
- Seamless hollow parts: hollow parts are seamless and do not require any bonding.
- Ideal for manufacturing simple shapes such as bottles: Simple shapes such as bottles can be produced at a fast rate and low cost.
Disadvantages of blow molding:
- Part geometry is limited and restricted to basic forms: blow molding is ideal for parts with simple geometry
- Tooling cost is very high: tooling is high and is approximately 6-10 times the cost of rotational molding tooling.
- Low volume production quantities are costly: due to setup costs, producing lower quantities drive prices higher.
- Surface finish is not aesthetic: parting lines can be pronounced and surface texture is not always desirable.
What are the advantages and disadvantages of Rotational Molding?
Advantages of rotational molding:
- Low cost tooling: tooling cost is low in comparison to blow molding due to the low pressures involved.
- Consistent wall thickness: because the process uses gravitational forces to spread the plastic inside a mold, parts form with uniform wall thickness.
- Double wall construction: double wall parts can be formed which are ideal for cases and containers.
- High strength and durability: structural features can be designed into parts providing additional strength and support for large flat surface areas.
- Seamless hollow parts: the parting lines on rotationally molded parts are discrete.
- Ability to mold complex geometry: design flexibility provides the ability to mold very complex and detailed assemblies.
Disadvantages of Rotational Molding
- Cycle times: the only disadvantage of rotational molding vs. injection molding and blow molding is the cycle times, however this can be overcome with multiple low cost tools.
See Also: Advantages and Disadvantages of Rotational Molding
Is Rotomolding Right for You?
When deciding whether rotomolding is the right process for you it is important to consider the following.
- Is low cost tooling an important factor?
- Does the design have a degree of complexity to it that prevents it from being blow molded?
- Does the project require a short production run to begin with and then ramp up afterwards?
If the answer to any of those is yes then rotomolding is the right process for your project. That is to say, if you are looking for a rotomolding company in California, contact us today for a free quote.
Most importantly, blow molding is ideal for simple tanks, however when it comes to manufacturing parts with more detail there can be additional tooling and process costs for secondary processes.
Roto Molding vs. Blow Molding |
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Specifications |
Blow Molding |
Rotational Molding |
| Uniform wall thickness | Wall thickness become inconsistent as the part diameter increases | Walls thickness is uniform throughout the part |
| Tooling | High quality CNC tools | High quality CNC tools or lower cost cast tools |
| Tooling Cost | Usually 6-10 times the cost of rotomolding tooling | 3 tooling grade options all lower than blow molding tooling costs. |
| Tooling Maintenance | Mold is under pressure and requires costly maintenance. Modifications come at a high cost. | Mold is under low pressure and may require minor maintenance. Modifications are relatively low in cost. |
| Tooling lead times | 11-12 weeks | 7-8 weeks |
| Cycle Times | Low cycle times provide a higher output per tool cavity | Higher cycle times provides lower output per tool cavity |
| Design Flexibility | Limited design flexibility and simpler part geometry | Flexibility in the design allows for undercuts, threaded inserts, graphics and various other complex features |
See also: Rotomolding Design Guidelines
Case Study – 50 Gallon Trash can
Roto Molding vs. Blow Molding Case Study – 50 Gallon Trash Can |
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| Cost Factors | Roto Molding | Blow Molding |
| Tooling Cost | $20,000 | $210,000 |
| Tooling maintenance Cost | $1000 / yr. | $5000 / yr. |
| Part Cost | $110 | $90 |
Design Flexibility in Rotomolding
The diagram below shows a design guideline for the Rotational Molding process.
- Features: There are various features that can be incorporated into a product. These include, male/ female threads, threaded inserts, graphics, raised lettering, ribbing structures and undercuts.
- Cost considerations: When making a part cost efficient it is important to take into consideration the quantity of inserts, tool pieces and part weight have an impact of the average cost of the final product.
Conclusion
In conclusion, rotational molding has a clear advantage with design flexibility and low cost tooling. Certainly, now that you have ready more about Roto Molding vs. Blow Molding, read more here about Rotational Molding vs. Injection molding.
If you are looking for a roto molding company and need expert advice contact our California headquarters at (877) 768-6585.
See Also Infographic About Rotational molding vs. Blow molding.